- Remove Gitlab::ImportExport::ProjectCreator from GitlabProjectsImportService
- Override ::Projects::CreateService params

First round of review, main changes:
- templates.title is human readable, #name will be passed around
- GitLabProjectImporterService has been renamed

Started implementation for the first iteration of
gitlab-org/gitlab-ce#32420. This will allow users to select a template
to start with, instead of an empty repository in the project just
created.

Internally this is basically a small extension of the ImportExport
GitLab projects we already support. We just import a certain import
tar archive. This commits includes the first one: Ruby on Rails. In the
future more will be added.